Foam materials have a wide variety of applications including fire-fighting, vapor suppression, and crop insulation, among others, and are commercially and industrially important. Currently, foaming materials are prepared by diluting a concentrate of a foaming composition and aerating the diluted solution by eduction or otherwise.
One commercially important class of foams includes aqueous film forming foams (AFFFs). Commercially available AFFF agents typically contain one or more fluorochemical surfactants, non-fluorinated surfactants, thickening agents and aqueous or non-aqueous solvent. The surfactants decrease the surface tension of the foam, increasing the spontaneous spreading of the aqueous film over the surface of non-polar solvents, and contribute to the bubble structure of the foam. The fluorosurfactants extinguish hydrocarbon fires by spreading a thin film over the surface of the fuel. AFFF products, like those used in firefighting, can attain long foam duration by incorporation of a thickening agent or polymer, such as xanthan gum, in the foam concentrate. Thickening agents are used to increase the viscosity and stability of the foam. The incorporation of a polymer into the foam helps retain water in the bubble structure, thereby increasing the drain time and stability of the foam. AFFF products frequently also contain hydrocarbon-based surfactants and are effective in covering the surface of and extinguishing hydrocarbon based fires.
A second commercially important class of foams includes alcohol-resistant aqueous film forming foams (AR-AFFFs). AR-AFFFs also typically contain one or more fluorochemical surfactants, non-fluorinated surfactants, and thickening agents but are designed to also extinguish alcohol and other water-soluble solvent fires by precipitating an alcohol-insoluble polymer, such as xanthan gum, on the surface of the fuel. When the polymer, which is dissolved in the foam solution, contacts a polar solvent, it comes out of solution, forming a cohesive membrane across the surface of the fuel, and extinguishes the fire. Additional foam application cools the membrane and contributes to further sealing of the fuel.
Many of the components typically included in a foam composition concentrate present drawbacks, however. Fluorochemical surfactants are known toxicants and are extremely difficult to remove from the environment. There is a need in the art for stable AFFF and AR-AFFF that do not rely on the use of fluorochemical surfactants. Polymer thickening agents can be difficult to hydrate without clumping; high shear mixing is usually required to sufficiently disperse the polymer particles so that each polymer particle can be fully hydrated. High shear mixing is a time consuming and industrial process, however, resulting in the current state of the art of foam compositions being sold in concentrate form that have been prepared utilizing high shear mixing conditions. The concentrate foam composition can be used to produce a foam either by mixing with water and entraining with air or educting directly through a water stream with the resultant foam either being short or long lived depending on the retention of water in the bubble structure. The use of a concentrate limits the amount of polymer that can be incorporated into the foam composition because beyond a certain amount of polymer the foam composition will become too viscous to be educted or easily diluted to form the foam solution.
The maximum level of polymer in a typical foam concentrate is approximately 1.5 weight percent (15 g/L) polymer to foam concentrate. At concentrations greater than 1.5 weight percent the polymer gels, causing mixing and educting problems that render the product unusable. The resulting use-concentration of a firefighting foam is 3 weight percent of foam concentrate mixed in water for an AR-AFFF 3×3 (3 weight percent for hydrocarbon fires, 3 weight percent for alcohol type fires) or 6 weight percent for an AR-AFFF 3×6 (3 weight percent for hydrocarbon fires, 6 weight percent for alcohol type fires). This produces a foam that is limited in stability by this maximum level of polymer attainable from a concentrate. A standard commercially available AR-AFFF 3×3 with the maximum 1.5 weight percent polymer level, diluted to the standard 3 weight percent, generally can only attain a maximum of 0.45 g/L polymer in the diluted mixed foam solution. There is a need in the art for polymer solutions and foam compositions that allow a sufficient amount of polysaccharide to be incorporated into the foam without requiring high shear mixing.